1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device.
2. Description of the Related Art
Owing to the demands of miniaturization of semiconductor devices, the thickness of photo-resist films is becoming increasingly smaller. Accordingly, it has become difficult to ensure a sufficient etching resistance only by a photo-resist film. In light of this problem, there has been proposed a pattern transferring technique utilizing a multilayer resist (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2006-140222). In general, a multilayer resist is formed of a lower film, an intermediate film, and an upper film (photo-resist film).
However, along with a further decrease in the thickness of photo-resist films, a problem arises in that a photo-resist pattern disappears when the photo-resist pattern is used as a mask in dry etching of the intermediate film. In this case, since that portion of the intermediate film which serves as a mask is etched, it is difficult to form an adequate pattern at the intermediate film. If wet etching is used for the same purpose, the photo-resist pattern may be prevented from disappearing. However, since wet etching is isotropic etching, in which the etching proceeds in a lateral direction as well, the photo-resist pattern cannot be faithfully transferred to the intermediate film. Conventionally, because of such a reason, it is difficult to form an adequate pattern at the intermediate film, and thus is also difficult to reliably form a device pattern, such as an interconnection pattern, with high accuracy.
The problem described above is caused not only in a case where a multilayer resist is used for patterning an etching target film, but also in a case where a photo-resist pattern formed directly on an etching target film is used as a mask for etching the etching target film.
As described above, conventionally, there is a problem in that, when a photo-resist pattern is used as a mask for etching an underlying film, it is difficult to form an adequate pattern.